Studies of volume overload (VO) of mitral and aortic regurgitation (MR and AR) show no benefit on LV remodeling using vasodilator drugs or renin-angiotensin system blockade. In the current project, we present preliminary data demonstrating the existence of matrix metalloproteinases (MMPs) within mitochondria and their activation with VO. The mitochondrial (mt) DNA haplotype of C57BL/6J compared to that of C3h/HeN mice have higher proton coupling and ROS generation. Therefore we hypothesize that the C57 mtDNA haplotype produces greater cardiomyocyte oxidative stress and bioenergetic dysfunction, mitochondrial MMP activation, and disruption of myofibrillar and mitochondrial structure in VO. ROS can act as signaling mechanisms to the nucleus. We also hypothesize that mitochondrial haplotype directs nuclear molecular signals that also produce a greater molecular inflammatory response and predict adverse LV remodeling and function in VO. We will use the C57 mouse with its nuclear background combined with C3H mtDNA (C57n:C3Hmt) mitochondrial nuclear exchange (MNX) mouse, to test whether mice with C3H mtDNA can rescue C57 from pathologic consequences of VO and vice versa in C3Hn:C57mt mice in the following specific aims. 1) Characterize the impact of mtDNA haplotype on cellular bioenergetics and LV function in VO. 2) Demonstrate that mtDNA haplotype determines increased mitochondrial oxidant production in VO and causes mitochondrial MMP activation. 3) Demonstrate that mtDNA haplotype influences nuclear molecular inflammatory response in the LV of mice subjected to the VO of ACF. This proposal with utilize the aortocaval fistula mouse model of VO, which integrates novel technology of measurements of bioenergetics of intact cardiomyocytes and oxidative stress in a MNX mouse model in which the mitochondrial (mt) DNA of one mouse strain is incorporated into the nuclear (n) genome of another (e.g., C57n:C3Hmt or C3Hn:C57mt).